/Engine/Plugins/VirtualProduction/Takes/Source/TakeTrackRecorders/Public/TrackRecorders/MovieSceneTrackRecorder.h
This is called when Recording actually starts happening. Tracks and Sections should have already been created during CreateTrack so this call simply informs you of:
void SetSectionStartTimecode ( const [FTimecode](API\Runtime\Core\Misc\FTimecode) & InSectionStartTimecode, const [FFrameNumber](API\Runtime\Core\Misc\FFrameNumber) & InSectionFirstFrame )